EFFECTS OF HUMAN ACTIVITIES ON THE INTERACTION OF ... - USGS
嚜激FFECTS OF HUMAN ACTIVITIES
ON THE INTERACTION OF
GROUND WATER AND SURFACE WATER
Human activities commonly affect the distribution, quantity, and chemical quality of water
resources. The range in human activities that affect
the interaction of ground water and surface water is
broad. The following discussion does not provide
an exhaustive survey of all human effects but
emphasizes those that are relatively widespread. To
provide an indication of the extent to which
humans affect the water resources of virtually all
landscapes, some of the most relevant structures
and features related to human activities are superimposed on various parts of the conceptual landscape (Figure 25).
The effects of human activities on the quantity and quality of water resources are felt over
a wide range of space and time scales. In the
following discussion, ※short term§ implies time
scales from hours to a few weeks or months, and
※long term§ may range from years to decades.
※Local scale§ implies distances from a few
feet to a few thousand feet and areas as large as a
few square miles, and ※subregional and regional
scales§ range from tens to thousands of square
miles. The terms point source and nonpoint source
with respect to discussions of contamination are
used often; therefore, a brief discussion of the
meaning of these terms is presented in Box M.
Agricultural Development
Agriculture has been the cause of significant
modification of landscapes throughout the world.
Tillage of land changes the infiltration and runoff
characteristics of the land surface, which affects
recharge to ground water, delivery of water and
sediment to surface-water bodies, and evapotranspiration. All of these processes either directly or
indirectly affect the interaction of ground water and
surface water. Agriculturalists are aware of the
substantial negative effects of agriculture on water
resources and have developed methods to alleviate
some of these effects. For example, tillage practices have been modified to maximize retention of
water in soils and to minimize erosion of soil from
the land into surface-water bodies. Two activities
related to agriculture that are particularly relevant
to the interaction of ground water and surface
water are irrigation and application of chemicals to
cropland.
54
Figure 25. Human activities and structures, as depicted
by the distribution of various examples in the conceptual landscape, affect the interaction of ground water
and surface water in all types of landscapes.
55
M
Point and Nonpoint
Sources of Contaminants
Contaminants may be present in water or in air as
a result of natural processes or through mechanisms of
displacement and dispersal related to human activities.
Contaminants from point sources discharge either into ground
water or surface water through an area that is small relative to
the area or volume of the receiving water body. Examples of
point sources include discharge from sewage-treatment
plants, leakage from gasoline storage tanks, and seepage
from landfills (Figure M每1).
Nonpoint sources of contaminants introduce
contaminants to the environment across areas that are
large compared to point sources, or nonpoint sources may
consist of multiple, closely spaced point sources. A nonpoint
source of contamination that can be present anywhere, and
affect large areas, is deposition from the atmosphere, both
by precipitation (wet deposition) or by dry fallout (dry deposition). Agricultural fields, in aggregate, represent large areas
through which fertilizers and pesticides can be released to the
environment.
The differentiation between point and nonpoint sources
of contamination is arbitrary to some extent and may depend
in part on the scale at which a problem is considered. For
example, emissions from a single smokestack is a point
source, but these emissions may be meaningless in a regional
analysis of air pollution. However, a fairly even distribution of
tens or hundreds of smokestacks might be considered as a
nonpoint source. As another example, houses in suburban
areas that do not have a combined sewer system have individual septic tanks. At the local scale, each septic tank may
be considered as point source of contamination to shallow
ground water. At the regional scale, however, the combined
contamination of ground water from all the septic tanks in
a suburban area may be considered a nonpoint source of
contamination to a surface-water body.
Figure M每1. The transport of contamination from a point
source by ground water can cause contamination of surface
water, as well as extensive contamination of ground water.
Waste site
of
ion
ect
flow
Dir
ter
-wa
und
gro
er
Riv
Contaminant
plume
56
IRRIGATION SYSTEMS
Surface-water irrigation systems represent
some of the largest integrated engineering works
undertaken by humans. The number of these
systems greatly increased in the western United
States in the late 1840s. In addition to dams on
streams, surface-water irrigation systems include
(1) a complex network of canals of varying size
and carrying capacity that transport water, in many
cases for a considerable distance, from a surfacewater source to individual fields, and (2) a drainage
system to carry away water not used by plants that
may be as extensive and complex as the supply
system. The drainage system may include underground tile drains. Many irrigation systems that
initially used only surface water now also use
ground water. The pumped ground water
commonly is used directly as irrigation water, but
in some cases the water is distributed through the
system of canals.
Average quantities of applied water range
from several inches to 20 or more inches of water
per year, depending on local conditions, over the
entire area of crops. In many irrigated areas, about
75 to 85 percent of the applied water is lost to
evapotranspiration and retained in the crops
(referred to as consumptive use). The remainder of
the water either infiltrates through the soil zone to
recharge ground water or it returns to a local
surface-water body through the drainage system
(referred to as irrigation return flow). The quantity
of irrigation water that recharges ground water
usually is large relative to recharge from precipitation because large irrigation systems commonly are
in regions of low precipitation and low natural
recharge. As a result, this large volume of artificial
recharge can cause the water table to rise (see
Box N), possibly reaching the land surface
in some areas and waterlogging the fields. For this
reason, drainage systems that maintain the level of
the water table below the root zone of the crops,
generally 4 to 5 feet below the land surface, are an
essential component of some irrigation systems.
The permanent rise in the water table that is maintained by continued recharge from irrigation return
flow commonly results in an increased outflow of
shallow ground water to surface-water bodies
downgradient from the irrigated area.
57
N
Effects of Irrigation Development
on the Interaction of
Ground Water and Surface Water
Nebraska ranks second among the States with respect
to the area of irrigated acreage and the quantity of water used
for irrigation. The irrigation water is derived from extensive
supply systems that use both surface water and ground water
(Figure N每1). Hydrologic conditions in different parts of
Nebraska provide a number of examples of the broad-scale
effects of irrigation development on the interactions of ground
water and surface water. As would be expected, irrigation
systems based on surface water are always located near
streams. In general, these streams are perennial and (or)
have significant flow for at least part of the year. In contrast,
irrigation systems based on ground water can be located
nearly anywhere that has an adequate ground-water
resource. Areas of significant rise and decline in ground-water
levels due to irrigation systems are shown in Figure N每2.
Ground-water levels rise in some areas irrigated with surface
water and decline in some areas irrigated with ground water.
Rises in ground-water levels near streams result in increased
ground-water inflow to gaining streams or decreased flow from
the stream to ground water for losing streams. In some areas,
it is possible that a stream that was losing water before development of irrigation could become a gaining stream following
irrigation. This effect of surface-water irrigation probably
caused the rises in ground-water levels in areas F and G in
south-central Nebraska (Figure N每2).
EXPLANATION
Surface-water
irrigation project
0
20
40 MILES
Figure N每1. Nebraska is one of the most extensively irrigated States in the Nation. The irrigation water comes from
both ground-water and surface-water sources. Dots are irrigation wells. (Map provided by the University of Nebraska,
Conservation and Survey Division.)
58
................
................
In order to avoid copyright disputes, this page is only a partial summary.
To fulfill the demand for quickly locating and searching documents.
It is intelligent file search solution for home and business.
Related download
- lesson outline for teaching readington township public
- chapter resource files editable impacts on the land
- warren hills regional school district warren hills
- explore your watershed national park service
- effects of human activities on the interaction of usgs
- core knowledge lesson plans
- vce outdoor and environmental studies units 1 2
- lesson 2 soil degradation and conservation
- module 2 educator s guide investigation 3 nasa
- chapter 14 unit notes moore public schools
Related searches
- the effects of video games on teens
- positive effects of the internet on education
- human impact on the environment
- human impacts on the environment
- human impact on the earth
- human impact on the environment article
- human impact on the environment articles
- human impacts on the atmosphere
- effects of human activities in our environment
- negative human impacts on the environment
- human impact on the ecosystem
- effects of air pollution on human health